This research will examine the importance of biological and physical causes of variation in the production of bioactive secondary metabolites by tropical seaweeds and invertebrates. The research has important biomedical consequences since it will focus on understanding what factors affect the yields of biomedically important marine natural products. First, differences in types and concentrations of secondary metabolites in different tissues, among individuals, at different ages and life history stages, and among populations of seaweeds and invertebrates will be examined. Facultative changes in chemical defenses will be examined for seaweeds, sponges, and soft corals exposed to: 1) increased grazing by fishes, mesograzers, and specialists predators; and 2) different resource levels of light and nutrients. The proposed research will provide information on chemical variation and its causes and the ability and timing of seaweeds and invertebrates to change their allocation of chemical defenses. The study will contribute to our limited knowledge of the chemical interactions of seaweeds and marine invertebrates, the physiological properties of marine natural products, and the relationship between natural adaptive functions of secondary metabolites and their biomedical potential. Bioactive metabolites will be incorporated into established testing programs (Univ. of Hawaii, UC Santa Barbara, Wayne State University Medical School) to determine their pharmacological activities in specific assays. Funding is requested primarily for personnel and supplies to carry out this research. This research program will provide educational opportunities for minority undergraduate and graduate (M.S. degree) students at the University of Guam, a predominantly undergraduate and minority institution with relatively large biology, nursing, and public health related programs.